The invention relates to heat sinks. More particularly, the invention relates to heat sinks used in personal computer systems.
Nearly all computer systems and most electrical power systems in the world have at least one element that produces heat. Frequently, this heat must be dissipated to the surrounding air. If this heat is not adequately dissipated, the heat may damage the heat-producing element, itself, or one of the nearby elements.
Sometimes, the heat-producing element is too small and does not conduct heat well enough to dissipate the heat as rapidly as necessary. In this case, it is necessary to attach a heat sink to the element. The heat sink, usually made of metal, has a much larger surface area than the element has and conducts heat very well. The excellent heat conduction properties of the heat sink allow it to quickly conduct heat away from the element, and the large surface area allows it to rapidly dissipate the heat to the surrounding air.
As the air surrounding the heat sink is heated up, it is necessary to blow the air away, so that there will always be cool air surrounding the heat sink. Therefore, many electrical systems provide a fan to blow air across the heat sink. The air blown by a fan is very turbulent due to the vortices created in the air by the spinning fan blades and by the interaction of the moving air with the non-moving air after the air passes through the fan. If the fan blows directly on the heat sink, then the turbulence aids in the dissipation of heat. This turbulence permits the air to circulate around the heat sink so the air can receive more heat than laminar, or linearly-flowing, air would receive. Additionally, this turbulence permits the heated air to mix with the cooler air, so the heat can diffuse through the air more quickly.
A system wherein the fan blows directly onto the heat-producing element experiences a localization of air pressure in the path where the fan blows. Other areas within the system receive less airflow, so heat-producing elements in those areas do not cool as easily. In a system enclosed within a housing unit, as a personal computer system is enclosed within a central processing unit (CPU) box, the fan does not need to blow directly onto the heat-producing elements. In this case, the fan may be situated to blow air out of the housing unit instead of into the housing unit. The passage of air through the unit, therefore, will be governed by the position of air intake vents in the side of the housing and by the position of elements within the housing. Air pressure is thus equalized throughout most of the housing because there is no particular path in which the fan blows, so the system cools more evenly. Additionally, more air is circulated through the housing unit than with an inward-blowing fan. With an inward-blowing fan here is high pressure inside the housing unit. This high pressure causes a back-pressure against the fan which prevents the fan from blowing air more efficiently than it would otherwise be capable of blowing. An outward-blowing fan creates a vacuum within the housing unit which may reduce the efficiency of the fan, but it is easier to compensate for this vacuum with additional vents in the side of the housing than it is to compensate for the high pressure of an inward-blowing fan. Therefore, air movement is more efficient with an outward-blowing fan than with an inward-blowing fan.
Although cooling may be more evenly distributed within a personal computer system in which the fan blows out of the box, the advantages from the turbulence created by the fan may be lost. Since the fan in this situation creates no vortices in the air within the housing, the airflow is much more laminar, or linear. The objects within the housing may create some disturbances in the airflow, but since the airflow is more evenly distributed within the housing, the turbulence thus created is not as significant as that created in the path of an inward-blowing fan. The air, therefore, does not circulate around the heat-producing elements very readily and the hot air does not quickly mix with the cooler air.
Therefore, there is a need to provide an electrical system housing and a heat sink which, together, take the benefits of an outward blowing fan (evenly distributed laminar airflow and greater airflow) and add the benefits of turbulence to the airflow.
To date, developments in heat sinks have been in two general areas: increasing the mass of the heat sink and increasing the surface area of the heat sink. These two development criteria have, of course, been offset by the constraints of the system in which the heat sink is to be utilized, e.g. available space.
Generally, a more massive object can conduct more heat across its length, and an object with more surface area can dissipate more heat to the surrounding air. The teaching, therefore, has been to build the most massive heat sink with the most surface area, so it can conduct more heat to its surface where the heat can be dissipated rapidly. No one, however, has yet optimized the configuration of the heat sink with the benefits of an outward-blowing fan and turbulence in the airflow.
FIG. 1 shows a cross section of a prior art heat sink 110 with a lot of mass and a large surface area. There are many heat sinks of this general type. This particular heat sink 110 is offered as an example of the problems inherent in this type of heat sink. The heat sink 110 in this case is an elongated metal member whose cross section at any point is that shown in FIG. 1. In heat sink 110, the cross section must be situated perpendicular to the direction of airflow so that air travels through channels 112 defined generally by planar members 114. The airflow, in order to flow through the channels 112, should ideally be laminar. Turbulent air would not flow well through the channels 112, so the advantages of turbulence are lost with this type of heat sink.
Additionally, this heat sink 110 is fabricated by a process of extrusion. This process requires extremely high pressure to pass the metal through the hole having the cross section shown in FIG. 1. After the extrusion, there is the additional finishing and straightening processes to be performed on this type of heat sink. Therefore, this process is extremely expensive and time consuming.
FIG. 2 shows a side view of another prior art heat sink 220 having a row of straight fingers 222 and a row of bent fingers 224. Heat sink 220 takes advantage somewhat of the benefits of the turbulence. The rows of fingers 222 and 224 permit turbulent air to circulate around them, but the prior art does not teach the optimization of the benefits of turbulence. The teaching of the heat sink in FIG. 2 requires that the rows of fingers 222 and 224 be too close together to permit air to circulate freely. Air circulating around one row of fingers interferes with air circulating around the other row. In laminar airflow, turbulence is generated in the air as it flows past the rows of fingers 222 and 224, but the turbulence generated by one row of fingers interferes with the turbulence around the other row reducing the efficiency of the circulating and mixing effects of turbulence, so the circulating and mixing benefits of turbulence are not optimized. Heat sink 220 may be placed in the airflow path of an inward-blowing fan, thus receiving added turbulence, but the benefits of an outward-blowing fan are lost, and it is generally accepted that this type of heat sink is not designed for use in turbulent airflow.
Another problem with the prior art heat sink 220 in FIG. 2 involves its method of fabrication. The sharp bend in the base 226 of the row of fingers 224 can produce necking in the base 226. Necking is the stretching and narrowing of the metal due to the bending procedure. Necking causes microscopic stress fractures in the metal in the base 226. These microscopic stress fractures impede the conduction of heat through the base 226 to the row of fingers 224. Thus, the efficiency of the heat sink 220 is reduced. Additionally, the narrowing of the metal provides less mass at the base 226, so less heat is conducted through the base 226.